Bushings having an annular rubber or elastomeric insert between a pair of concentric sleeves have been known and used for many years. Generally, the bushing is used for mounting a second member, e.g. a motor, to a first member, e.g. an automobile frame, where the members must move relative to each other. The inner sleeve is secured, for example by a pin or bolt, to the first member, and the outer sleeve is secured to the second member. The relative axial, lateral, and rotational movement between the two members is accomodated by the elastomeric or rubber annular insert.
By radially compressing the rubber insert between the inner and outer sleeves, increased load bearing and lifetime can be achieved. In such a bushing the molded rubber insert is cured prior to assembly and held in place under radial compression; the restorative tendencies of the rubber aid in preventing relative motion between the insert and the sleeves.
A number of methods and apparatus have been used for assembling the elastomeric insert for radial compression between the inner and outer sleeve members. See, for example, U.S. Pat. Nos. 2,690,001 and 2,660,780. Generally, apparatus for assembling rubber-metal bushings includes a support member upon which is mounted an open ended guide funnel. A clamping mechanism is located at the small end of the funnel and in axial alignment therewith, for positioning the outer sleeve. A plunger is provided in axial alignment with and advanceable axially into the large end of the funnel face. A mandrel is located at the opposite end of the support and in an axially aligned position with the funnel member. The mandrel is usually of a tapered or frusto conical profile with its smallest diameter approximately equal to or smaller than the annular opening in the rubber insert and its larger diameter substantially equal to the outside diameter of the inner sleeve. The inner sleeve member is positioned behind the larger diameter of the mandrel for insertion into the insert.
To assemble the bushing, the annular elastomeric insert is positioned between the plunger and large end of the funnel, and is inserted into the outer sleeve by means of the plunger forcing the insert through the large end of the funnel for compression into the outer sleeve positioned at the opposite end of the funnel. The mandrel, with the inner sleeve positioned behind it, is then forced through the annular opening in the insert to position the inner sleeve member therein. The plunger and mandrel are retracted to expose the completed assembly.
Improved apparatus has been proposed for the construction and assembly of rubber-metal bushings. See, for example, U.S. Pat. No. 3,555,655. In this improved apparatus, a mandrel assembly and a nesting assembly are axially aligned and spaced apart from one another. The mandrel assembly comprises an elongated enclosed mandrel cylinder and a piston therein. A first abutment surface is provided to contact one end of the elastomeric insert. Through the abutment surface extends an elongated rod, one end of which is joined to the piston an the other end of which forms a head including a tapered tip and a frusto conical portion, the diameter of which decreases toward the aperture through which it extends. The junction between the tip and frusto conical portion forms a shoulder for engagement with one end of the inner sleeve. The first abutment surface and the mandrel are both capable of independently moving to and from a nesting assembly. The nesting assembly includes an annular stationary holder for the outer sleeve of the bushing. A plunger is provided which is movable through the holder in a direction to and from the mandrel, and includes an insert abutment shoulder and a positioning pin for the inner sleeve. In operation, the mandrel including the tip and conical portion first passes through the free or unconstricted inner annular opening of the elastomeric insert, after which the abutment surface of the mandrel engages the insert and forces it into the outer sleeve which is positioned in the nesting assembly. As the first abutment surface of the mandrel engages and forces the annular insert into the outer sleeve, the tapered tip and shoulder of the frusto conical portion engages the inner sleeve member positioned on the plunger of the nesting assembly. The plunger and mandrel are then forced back through the annular opening in the insert to position the inner sleeve therein.
Both types of devices require a mandrel for radially enlarging the opening in the compressed elastomeric insert for the insertion of the inner sleeve member. Both means of assembling the inner sleeve require a large axial force not only because of the high radial forces of the compressed insert, but also because of the inherently high axial frictional forces of the elastomeric or rubber insert. In addition to the high axial forces required, the operation of assembling the bushing, particularly the inner sleeves, produces high noise levels which are not satisfactory.